1. Field of the Invention
This invention relates to methods of and apparatus for storing digital video signals.
2. Description of the Prior Art
Requirements exist, in for example a slow motion video signal processor, to store about one second of digital video signal in random access memory. The amount of digital data involved is very large, and this requires a correspondingly large amount of random access memory. One way of reducing the amount of random access memory required (or alternatively of increasing the duration of video signal which can be stored) is to reduce the length of the words forming the digital data by using differential pulse code modulation. With this technique, it is for example possible to reduce the length of each word in the digital data from the usual eight bits to five bits, without severe loss of quality in the subsequently reproduced picture.
However, this reduction in the word length will not necessarily always be required, and this introduces the problem of providing a video signal store which is capable of efficiently storing a digital video signal, the word length of which may vary. Thus, if the standard word length is eight bits, then the usual video signal store will of course have provision for storing the eight bits of each input word. If, however, the length of the input words is sometimes reduced to say five bits, then the usual video signal store can be arranged to store the five bits of each input word, but will leave empty the storage locations for the remaining three bits not now present. In other words, many storage locations will not be used, and there will be no increase in the duration of video signal which can be stored.